do I make my file size small enough to upload? I have the pixel dimensions right and I've tried saving as the lowest possible quality and it's still like, twice as large as it needs to be. This shouldn't be hard.

_________________[...]then i pooped pink sparkles out of sheer hatred. -allularpunk

I start by opening a picture (obvs). Then I use rectangle select and change it from normal selection mode to fixed ratio, and set the ratio to 5 x 7. Then I draw the rectangle over what I want as my avatar. I use the Move Selection arrow to center it up all pretty. Then I crop to selection, then resize to 100 x 140. I nearly always save as PNG and you can move the quality slider a little down if he filesize is still somehow too big. Tada!